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From Galápagos albatrosses to polar bears, primates to orangutans, various animals appear to kiss. Now, researchers suggest that ancient hominins did it too – and might even have locked lips with modern humans.

Shared Microbial Evidence

It is not the first time scientists have suggested Neanderthals and Homo sapiens were closely connected. In previous studies, scientists have found modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the two species split, suggesting they swapped saliva.

"Likely they were kissing," she said, adding that the concept chimed with studies that has revealed people of non-African ancestry contain Neanderthal DNA in their genome, revealing genetic mixing was at play.

Intimate Interpretation

"It certainly puts a different perspective on ancient interactions," Brindle commented.

Writing in the publication a scientific periodical, Brindle and colleagues report how, to explore the evolutionary origins of intimate contact, they first had to develop a description that was not restricted by how humans kiss.

Defining Kissing

"Previously there were some previous attempts to describe a kiss, but it's largely focused on humans, which implies that basically other animals do not engage in this. Now we know that they likely engage, it may appear different from what human kissing resembles," explained the evolutionary biologist.

However, she said some behaviors that resembled kissing were something rather different – such as the chewing and food sharing, or "kiss-fighting", seen in fish known as certain marine animals.

As a result the team developed a definition of intimate contact based on social behaviors involving directed mouth-to-mouth contact with a member of the same species, with some movement of the mouth but absence of nutrition.

Research Approach

Brindle explained they concentrated on accounts of intimate behavior in primates from Africa and Asia, including primates, apes and great apes, and employed digital recordings to verify the reports.

Scientists then integrated this information with information on the evolutionary relationships between extant and extinct species of such primates.

Historical Origins

The team say the results suggest intimate contact developed somewhere between 21.5 million and 16.9 million years ago in the predecessors of the great primates.

The position of Neanderthals on this evolutionary lineage suggests it is probable they, too, indulged in a intimate act, the researchers say. But the behavior might not have been confined to their specific group.

"The fact that modern people engage intimately, the fact that we currently have demonstrated that ancient relatives probably kissed, suggests that the both groups are also likely to have kissed," the researcher noted.

Biological Importance

Although the evolutionary explanation is discussed, Brindle explained intimate contact could be employed in reproductive situations to possibly enhance reproductive success or help choose between mates, while it could assist reinforce bonding when used in a platonic way.

Another expert in the behavior of great apes commented that as kissing behavior was seen in a wide range of primates it was logical its origins extend far into our ancient history, and an analysis of different forms of kissing among a broader range of species might extend its origins back further still.

"Things that we think of as characteristics of our species, like kissing, are not exclusive to us if we examine carefully at other animals," he said.

Social Elements

An archaeology expert said that intimate contact had a social component as it was not universal to all human groups.

"However, as humans we thrive or fail on the strength of our emotional bonds, and methods of promoting trust and intimacy will have been important for millions of years," the professor stated. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a rather ruthless and aggressive past, but actually it ought to be no surprise that ancient hominins – and even them and our human ancestors collectively – kissed."